The present invention concerns a bending and squeezing blade for sheet metal bending and squeezing machine and a machine utilising the aforesaid blade.
For bending the edges of sheet metal, bending machines are commonly used in which the edge of the sheet metal to be submitted to bending is squeezed between a fixed bending counter blade and a mobile blank holder above it.
The operation of bending of the edge of the sheet metal is carried out by a bending device that has one or more bending blades that collaborate with the fixed counter blade and the blank holder to actuate the upward and/or downward bending of the edge of the sheet metal, at 90xc2x0 or more with respect to the resting plane of the sheet metal.
In particular, the sheet metal is bent upward owing to the action of a bending blade that is moved from bottom to top in order to carry out, in combination with the fixed counter blade and the blank holder, the upward bending of the sheet metal at 90xc2x0 and then, if desired, it is moved also horizontally in order to carry out, in combination with the blank holder, an additional bending of the sheet metal until it reaches a bending angle greater than 90xc2x0.
However, the configuration of the blank holder does not allow the aforesaid bending blade to realise bending angles above a certain limit, usually of 120xc2x0-150xc2x0, and in particular it does not allow to reach an angle of 180xc2x0, corresponding to the complete squeezing of the folded edge of the sheet metal on the remaining part of the same sheet metal.
In view of this state of the art, object of the present invention is to realise a bending blade that is configured in such a way as to be able to carry out not only the bending but also the 180xc2x0 squeezing of the edge of the sheet metal.
Another object is to realise a bending machine that is suitable to carry out the bending and the squeezing of the edge of a sheet metal through the aforesaid blade.
According to the invention such object is attained with a bending blade characterized in that it comprises a bending tooth provided with a head surface that is suitable to engage the edge of a sheet metal in order to carry out its bending at 90xc2x0 and with a foot surface that is suitable to engage the edge of the sheet metal folded at 90xc2x0 to carry out its additional bending at an angle greater than 90xc2x0 and its possible squeezing on the remaining part of the sheet metal up to an angle substantially equal to 180xc2x0.
The aforesaid blade is preferably utilised to bend the edge of the sheet metal upward at an angle equal to or greater than 90xc2x0 and then, if desired, its squeezing on the remaining part of the sheet metal. In order to be able to carry out the operation of squeezing it is obviously necessary to previously lift the blank holder from its engagement with the fixed counter blade. The sheet metal thus remains supported only on the counter blade and, for some types of sheet metal, a movement of the sheet metal can not be excluded that can jeopardise the execution of a correct squeezing of the folded edge of the same.
In order to obviate this possible inconvenience it is therefore provided that the blank holder is equipped with a pressing member that is operable in such a way as to be able to project downward from the foot of the blank holder so as to engage and retain the sheet metal on the counter blade by pressure.